1. Field of the Invention
The present invention relates to agents added to agricultural chemicals to be sprayed to crops for the purpose of reducing drift of the chemicals away from the target agricultural acreage. More particularly, the present invention relates to lecithin-containing drift reduction compositions which aid in the deposition onto and penetration into plants by aqueous sprays applied to agricultural acreage.
2. Description of the Related Art
The spraying or discharge of aqueous mixtures and solutions is important to a wide variety of agricultural crops, and involves the distribution of pesticides (including insecticides and larvaecides), herbicides, fertilizers and other agricultural products to crops and soil. However, when substantial amounts of the spray are present in the form of mistxe2x80x94i.e., fine droplets typically less than 141 microns in diameterxe2x80x94effectiveness is reduced as the mist drifts outside the area targeted for coverage. Indeed, spray droplet-size is a major factor contributing to drift. So, although smaller droplets might theoretically provide better coverage of a target area, they are more prone to drift than larger droplets.
Spray and discharge drift can prevent a substantial portion of a chemical from reaching its intended target, requiring more of the chemical to achieve adequate coverage of the target and increasing environmental pollution. For agricultural chemicals in particular, unwanted drift from the spray and discharge of herbicides and pesticides can pose a hazard to nearby crops, water supplies and livestock. Unwanted drift can also substantially increase the cost of chemical applications when necessitating repeat applications to compensate for under-treated crops.
Past research efforts to reduce spray drift have focused on improvements in the equipment used to spray or discharge aqueous mixtures on target areas. Several spray nozzle designs, for example, have been developed to optimize spray patterns and droplet size distributions. However, the most promising drift control techniques continue to be the use of additives and agents to reduce the fraction of fine droplet particles formed during the atomization of aqueous mixtures.
Experimentation has shown that the most effective drift control agents possess a number of important characteristics. Foremost, effective drift control agents significantly reduce the number of fine droplets in a spray or discharge. Effective drift control agents do not degrade or deactivate active ingredients such as pesticides, herbicides and the like. Effective drift control agents are slow to separate into a separate liquid phase on standing and during storage, and are environmentally friendly and cost efficient. Effective drift control agents need to be relatively resistant to high shear process conditions created by pumping solutions at high pressure through spray nozzles, atomizers and nebulizers.
Conventional drift control agents and additives include high molecular weight polymers that tend to increase the viscosity of an aqueous mixture or solution, hindering the atomizing mixture from breaking up into fine droplets. In the agriculture industry, for example, long chain polyacrylamides are routinely added to spray tanks as a drift reduction agents.
Unfortunately, high molecular weight, long chain polymers like polyacrylamides rapidly become less viscous when exposed to high liquid shear stresses commonly found in agricultural equipment like flow controllers, turbine metering systems, pumps, aerial spray nozzles, and so forth. The loss of polymer viscosity, called shear degradation, prevents drift control polymers from effectively suppressing fine droplet production throughout a spray application run. This is because shear degradation of drift control agents is dynamic and the polymer viscosity continually decreases the longer the drift control agents remain in a high shear stress environment. Adding additional drift control agent to compensate for the lower viscosity creates another problemxe2x80x94the aqueous mixture will start out too viscous at the beginning of a spray or discharge, reducing coverage efficiency.
Coverage efficiency strongly depends on the viscosity of the aqueous mixture. When viscosity gets too high coverage efficiency is reduced, requiring more solution to cover the same area as a less viscous liquid. Moreover, if the increased viscosity has resulted in a greater distribution of large-sized droplets, then the droplets have a tendency to bounce upon application. Effectiveness of foliar applications can be decreased when large droplets bounce off plant leaves and onto the ground.
U.S. Pat. No. 5,550,224 to Hazen entitled xe2x80x9cGuar as a Drift Control Agentxe2x80x9d discloses the use of guar and guar derivatives as drift control agents that are not affected by shear degradation. Guar is a nonionic polysaccharide that maintains its properties over a wide pH range. The guar polysaccharide is a complex carbohydrate polymer composed of essentially a straight chain of mannose units with single-membered galactose branches; chemically classified as a polygalactomannan.
In Hazen, guar compounds were added in small amounts (from 0.075% to 0.275% weight per unit volume (w/v) to aqueous mixtures, with the mixtures retaining a Newtonian fluid behavior similar to pure water. Despite having Newtonian characteristics, the aqueous guar mixtures in Hazen had significantly lower percentages of fine droplets (i.e., droplets smaller than 150 microns) than pure water. Moreover, the aqueous guar mixtures, as reported by Hazen, appeared substantially unaffected by shear forces and shear degradation, similar to pure water.
Soya lecithins, which have been reported to have drift control properties for aqueous mixtures, are surfactants used to enhance the activity and effectiveness of agricultural chemicals in aqueous mixtures. U.S. Pat. No. 4,666,747 to Quinn entitled xe2x80x9cSpray Method and Formulation for use thereinxe2x80x9d shows aqueous aerosol sprays containing soya lecithins have a smaller percentage of droplets with diameters of 100 microns or less compared to similar sprays lacking soya lecithins. Quinn, however, does not examine how soya lecithins hold up under high shear stress.
Of course soya lecithins are widely used in agricultural. U.S. Pat. No. 3,682,653 for xe2x80x9cGrain Conditioner-Modifier Chemical Combinationxe2x80x9d granted Aug. 8, 1972, describes a then-novel grain conditioner containing lecithin, a food grade acid and water. The preferred food grade acid is identified as propionic acid whose purpose is to reduce the lecithin pH and accomplish immediate dispersibility of the lecithin-acid chemical in water, thereby enhancing the well known and superior penetration and lubrication qualities.
One lecithin containing product presently available from Drexel Chemical Co. is PAS-800(trademark), a mixture of phosphatidylcholine and methylacetic acid also described as containing 1.2 diacyl-SN-glycero-3-phosphorylcholine and propionic acid. It is marketed as an agricultural penetrant, acidifier and surfactant. When mixed 1% w/w with tap water, its pH has been measured as an acidic 4.02. Product label directions at recommended use rates teach application by ground or aerial equipment. Similarly, LI-700(copyright), available from Loveland Industries, Inc., is another agricultural product identified for use as a surfactant, penetrant and acidifier. It is described as containing phosphatidylcholine, methylacetic acid and alkyl polyoxyethylene ether. When mixed 1% w/w with tap water, its pH has been measured as an acidic 3.49. There are numerous lecithin/propionic acid compositions available having a similarly acidic pH when so diluted in water.
Despite their use as a component of agricultural spray products, these acidic, lecithin-containing products do not optimally control drift. Accordingly, there remains a need for effective drift control agents for environments where shear degradation is continuously changing the ability of the drift control agent to maintain a particular mixture viscosity.
It has now been discovered that certain substantially neutral, lecithin-containing formulations can be utilized in an aqueous mixture or solution as drift control agents with improved drift reduction resulting from optimized droplet size distribution. The lecithin-containing formulations of the present invention possess the highly desirable characteristics of efficient drift control agents and maintain these properties under prolonged high shear stress conditions that are commonly encountered during commercial spraying,
The drift control agents of the present invention contain lecithin, a methyl ester (e.g., a methylated seed oil) which functions as a viscosity modifying agent and a non-ionic surfactant which functions as a water dispersing agent. When mixed 1% w/w in tap water, the pH of the resulting composition is substantially neutral (i.e., from 6.0 to 8.0). More preferably, the pH of a 1% w/w in water is 6.5 to 7.5, with the most preferable pH range of from 6.8 to 7.2. In a preferred embodiment, lecithin constitutes from about 40% to about 60% by weight of the drift control agent, the methylated seed oil (or equivalent) constitutes from about 20% to about 30% by weight of the agent, and the non-ionic surfactant constitutes about 20% to about 30% by weight of the agent. In a more preferred embodiment of the present invention, the non-ionic surfactant comprises polyoxyethylene ether. In the most preferred embodiment, the methyl ester is methyl soyate and the non-ionic surfactant is Tomadol(trademark), and even more preferably Tomadol(trademark) 1-5. The most preferred formulation contains, by weight, approximately 50% lecithin, approximately 25% of the methylated seed oil and approximately 25% polyloxyethylene ether.
In other embodiments of the drift reduction agents of the present invention, 0-5% of an anti-foam agent, preferably 1-3% of the anti-foam agent, and most preferably about 2% of an anti-foam agent are also present, together with from 0-25% of a glycol, preferably 5-20% of a glycol, and most preferably 12-15% of the glycol. Diethylene glycol is a preferred glycol and SAG-47 is a preferred anti-foam agent.